• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.4
• /
• pp.709-718
• /
• 2017

This paper proposes the guidance laws for an agile turn of air-to-air missiles during the initial boost phase. Optimal solution for the agile turn is obtained based on the optimal control theory with a simplified missile dynamic model. Angle-of-attack command generating methods for completion of agile turn are then proposed from the optimal solution. Collision triangle condition for non-maneuvering target is reviewed and implemented for update of terminal condition for the agile turn. The performance of the proposed method is compared with an existing homing guidance law and the minimum-time optimal solution through simulations under various initial engagement scenarios. Simulation results verify that transition to homing phase after boost phase with the proposed method is more effective than direct usage of the homing guidance law.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2007.06a
• /
• pp.323-326
• /
• 2007

When traveling on real road network, it generally takes less travel time in a near straight path than a zig-zaged path with same source and destination. In order to making a left(right/u) turn, the delay should be required to decrease the speed. The traffic signal waiting time of left(right/u) turn is probably longer than straight driving. In this paper, we revise the previous hierarchical path finding algorithm to reduce the number of turns. The algorithm proposed in this paper complied with a hierarchical $A^*$ algorithm, but has a distinct strategy for edge weight. We define an edge that makes a turn as a turn-edge and give the turn-edge lower weight to maintain the straightness of the whole path.

• English Language & Literature Teaching
• /
• v.13 no.4
• /
• pp.33-58
• /
• 2007

The present paper aims at comparing the two modes of CMC - synchronous and asynchronous - in terms of discourse markers used in turn-initial positions. It further attempts to examine the viability and limitations of these two modes of CMC in fostering EFL learners' face-to-face conversation skills. For these purposes, the present study analyzed 33 Korean EFL learners' Web chat and E-mail exchange data. Discourse markers in the participants' Web chat transcripts and those in their E-mail transcripts were identified and then compared in terms of their frequency and functions. The analysis revealed that the participants show difference in their preference for discourse markers depending on the modes of CMC. Also, the functions of discourse markers used for Web chat showed were strikingly different from those for e-mail. Especially, e-mail discourse markers revealed greater discrepancy from the markers in face-to-face conversation. The differences were found to be attributable to the time factor involved with the turn-taking systems of the two modes of CMC, especially the degree of instantaneousness in their turn-taking. Findings suggest that the turn taking skills and discourse marker use in CMC is not applicable to face-to-face conversation contexts. Pedagogical implications are discussed.

• Progress in Superconductivity and Cryogenics
• /
• v.20 no.3
• /
• pp.15-20
• /
• 2018

No-insulation (NI) pancake magnets are fabricated using Rare earth-Barium-Copper Oxide (REBCO) coated conductor (CC) tapes, which enabled a very compact magnet in the aspects of high critical current density ($J_c$) and high mechanical strength by removing insulation and allowing thinner stabilizer. They have also advantages such as self-quench protection. Therefore, it does not need quench detection and protection that can be very challenging in a high critical temperature ($T_c$) superconducting magnet technology. Recently, it was reported that the NI REBCO CC magnets have some drawbacks of long charging time and high field ramp loss which will be a concern in the operation of cryocooled magnets. These issues are related to the turn-to-turn contact resistivity and can be released by managing it. This is also closely related to the activity of reducing the contact joint resistance in the case of CC joints for long length CC fabrication. Therefore, in this study, the turn-to-turn contact resistance ($R_c$) at the CC contact part of differently stabilized CC tapes was measured. The behaviors of $R_c$ at CC contact parts according to the applied contact pressure were investigated. The range of $R_c$ measured for CC tapes adopted will provide fundamental data for design and fabrication of the CC NI coils.

• Proceedings of the KIPE Conference
• /
• 2003.07b
• /
• pp.677-680
• /
• 2003

The control of the SRM(Switched Reluctance Motor) is usually based on the non-linear inductance profiles with positions. So determination of optimal switching angle is very different. we present self-tuning control of SRM for maximum torque and efficiency with phase current and shaft position sensor During the sample time, micro-controller checks the number of pre-checked pulse. After micro-controller calculates between two data, it move forward or backward turn-off angle. When the turn-off angle is fixed optimal turn-off angle, turn-on angle moves forward or backward by a step using self-tuning control method. And then, optimal turn-off angle is searched once again. As such a repeating process, turn-on/off angle is moves automatically to obtain the maximum torque and efficiency. The experimental results are presented to validate the self-tuning algorithm.

• Journal of Power Electronics
• /
• v.18 no.3
• /
• pp.892-901
• /
• 2018

SiC MOSFETs have been used to improve system efficiency in high frequency converters due to their extremely high switching speed. However, this can result in undesirable parasitic oscillations in practical systems. In this paper, models of the key components are introduced first. Then, theoretical formulas are derived to calculate the switching oscillation frequencies after full turn-on and turn-off in clamped inductive circuits. Analysis indicates that the turn-on oscillation frequency depends on the power loop parasitic inductance and parasitic capacitances of the freewheeling diode and load inductor. On the other hand, the turn-off oscillation frequency is found to be determined by the output parasitic capacitance of the SiC MOSFET and power loop parasitic inductance. Moreover, the shifting regularity of the turn-off maximum peak voltage with a varying switching speed is investigated on the basis of time domain simulation. The distortion of the turn-on current is theoretically analyzed. Finally, experimental results verifying the above calculations and analyses are presented.

• Journal of the Korean Society of Safety
• /
• v.21 no.2 s.74
• /
• pp.52-56
• /
• 2006

This paper describes the methods for the detection of shorted-turn in the rotor of a cylindrical synchronous generator. A search coil is installed in the air-gap to detect the shorted-turn. The occurrence of a fault in the rotor winding results in a decrease of the induced voltages in the stator. And the magnitude of the rotor flux can be estimated by using the search coil and the estimated stator voltages respectively. And the magnitude of the estimated rotor flux is used for discriminating the rotor windings short or not by detecting the magnitude of the rotor flux. The method using a search coil located in the air-gap can detect not only the occurrence of a turn fault but also its position in the rotor winding. But the method using the estimated stator voltages gives the magnitude of the rotor flux, and only the number of a short-turn.

• Korean Journal of Applied Biomechanics
• /
• v.16 no.2
• /
• pp.65-73
• /
• 2006

The aim of this study was to find out the differences of Kinematics factors from touching down the vaulting board to landing when techniques of 1/1Turn and Tucked were performed on the old vaulting horse and on the new vaulting table. Three national representative men gymnasts were sampled for this study. Three dimension motion analyses by means of six Sony PD-150 video cameras with the velocity of 60 fps were used As a result of analyzing the kinematic data from two kind of vaulting table, the following conclusions were made. 1. The performing time from taking off the vaulting horse to landing(phase 4) in the 1/1 Turn technique on the new vaulting table was significantly longer than that of the old vaulting horse, while the time from contacting to taking off the vaulting horse on the new vaulting table was shorter than that of the old vaulting horse in both and the Tucked techniques. 2. The vertical release COG velocity was faster on the new vaulting table compare to the old vaulting horse in the all kind technique. However the horizontal release COG velocity of the 1/1 Turn technique was faster a little in the old vaulting horse compare to the new vaulting table.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.05c
• /
• pp.213-216
• /
• 2003

Recently a new high power device GCT (Gate Commutated Turn-off) thyristor has been successfully introduced to high power converting application areas. GCT thyristor has a quite different turn-off mechanism to the GTO thyristor. All main current during turn-off operation is commutated to the gate. Therefore, IGCT thyristor has many superior characteristics compared with GTO thyristor; especially, snubberless tum-off capacibility and higher turn-on capacibility. The basic structure of the GeT thyristor is same as that of the GTO thyristor. This makes the blocking voltage higher and controllable on-state current higher. The turn-off characteristic of the GCT thyristor is influenced by the minority carrier lifetime and the performance of the gate drive unit. In this paper, we present turn-off characteristics of the 2.5kV PT(Punch-Through) type GCT as a function of the minority carrier lifetime and variation of the doping profile shape of p-base region.

• Progress in Superconductivity and Cryogenics
• /
• v.20 no.4
• /
• pp.26-30
• /
• 2018

The turn-to-turn contact resistance of 2G high temperature superconducting (HTS) coils with metal insulation (MI) is closely related to the stability of the coils, current charging rate and delay time [1]. MI coils were fabricated using five kinds of metal tapes such as aluminum (Al) tape, brass tape, stainless steel (SS) tape, copper (Cu)-plated tape and one-sided Cu-plated SS tape. The turn-to-turn contact surface resistances of co-winding model coils using Al tape, brass tape, and SS tape were 342.6, 343.6 and $724.8{\mu}{\Omega}{\cdot}cm^2$, respectively. The turn-to-turn contact resistance of the model coil using the one-sided Cu-plated SS tape was $ 248.8{\mu}{\Omega}{\cdot}cm^2$, which was lower than that of Al and brass tape. Al or brass tape can be used to reduce contact resistance and improve the stability of the coil. Considering strength, SS tape is recommended. For strength and low contact resistance, SS tape with copper plating on one side can be used.